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Search Index (SI)

Last updated July 20, 2025

Search Index (SI) is a web performance and SEO-readiness metric that measures how well a page is prepared for discovery and inclusion in search engine indexes. It focuses on metadata completeness, crawlability, internal linking, and structured content — all crucial for organic visibility.

SI complements Core Web Vitals by addressing a page’s technical and semantic structure. A fast page that’s not indexable still won’t rank. This metric helps expose those gaps.

What it measures

The Search Index (SI) score reflects the completeness and correctness of SEO-critical signals, such as:

  • Presence of metadata — like <title>, <meta name="description">, and <link rel="canonical">
  • Proper indexing directives — including <meta name="robots"> and robots.txt rules
  • Semantic HTML — usage of <h1>, <article>, and other structural tags
  • Structured data — like schema.org JSON-LD blocks
  • Internal links — ensuring pages aren’t orphaned
  • Inclusion in sitemap.xml

The goal is to ensure a search engine can crawl, understand, and rank the page effectively.

Why it matters (UX/SEO impact)

Pages that fail to appear in search results often suffer from incomplete SEO foundations, not just slow performance. SI highlights those technical blind spots.

Consequences of low SI:

  • Pages not indexed or ranked
  • Missing metadata in search snippets
  • No rich results or structured enhancements
  • Content excluded from internal search or sitelinks

Search Index is especially critical for large sites, SPAs, and dynamically-rendered content — where indexation issues are common.

Relation to other Web Vitals

  • FCP/LCP/CLS measure loading and visual performance
  • SI evaluates discoverability and SEO health

SI answers the question: “Can search engines understand and index this content?” — while Web Vitals focus on UX after load.

Common Causes of Poor SI

  • Missing or duplicate <title> or <meta description>
  • Incorrect noindex directives
  • Blocked by robots.txt
  • Lack of semantic elements (e.g., no <h1>, <article>)
  • Unlinked pages (orphaned URLs)
  • No structured data or sitemap reference

How Search Index is Measured

SI is calculated by scanning the DOM and server response for expected SEO features. Each expected signal contributes to the total score, which is normalized between 0 and 1.

    

  1. SI Score = valid_signals / expected_signals
    2. 

  2. // Example: 9 valid out of 10 signals = 0.9
    3.

Tools like Testdom.io use headless browsers to evaluate the rendered output and server headers, ensuring both static and dynamic content is tested.

What is a Good SI Score?

  • Good: ≥ 0.9
  • Needs Improvement: 0.7 – 0.89
  • Poor: < 0.7
Score Scale
0.9
0.7

Target a score of 0.9+ on 75% of pages to ensure solid SEO visibility.

How to Improve Search Index

1. Add and Validate Metadata

Ensure every page includes a unique <title> and description.

    

  1. <title>Compare Fitness Trackers | GearZone</title>
    2. 

  2. <meta name="description" content="Discover the top-rated fitness trackers and smartwatches of 2025.">
    3.

2. Avoid Noindex and Robots.txt Blocks

Allow search engines to index the page unless intentionally excluded.

    

  1. <meta name="robots" content="index, follow">
    2. 

  2. // robots.txt
    3. 

  3. User-agent: *
    4. 

  4. Disallow:
    5.

3. Add Structured Data

Use JSON-LD format to help Google extract rich results.

    

  1. <script type="application/ld+json">
    2. 

  2. {
    3. 

  3.   "@context": "https://schema.org",
    4. 

  4.   "@type": "Product",
    5. 

  5.   "name": "Smartwatch X",
    6. 

  6.   "brand": "GearZone"
    7. 

  7. }
    8. 

  8. </script>
    9.

4. Link and Index All Pages

Internally link to all indexable pages and add them to your sitemap.

    

  1. <link rel="sitemap" type="application/xml" href="/sitemap.xml" />
    2.

5. Use Semantic HTML

Wrap content in structural tags that help crawlers understand layout and hierarchy.

    

  1. <article>
    2. 

  2.   <h1>Best Wireless Earbuds for 2025</h1>
    3. 

  3.   <p>Explore the latest picks for battery life, fit, and audio quality.</p>
    4. 

  4. </article>
    5.

Monitoring and Continuous Testing

Platforms like Testdom.io can help you monitor SI score across time and environments:

  • Spot regressions after deployments
  • Validate staging vs. production SEO signals
  • Get alerts for missing or blocked metadata

Sample Puppeteer-based scan logic:

    

  1. const hasTitle = !!document.querySelector('title');
    2. 

  2. const hasMetaDesc = !!document.querySelector('meta[name="description"]');
    3. 

  3. console.log('Search Index Ready:', hasTitle && hasMetaDesc);
    4.

Optimizing SI ensures your site isn’t just fast — it’s findable.